This is a message of sincere thanks to Larry Bible for walking me through the necessary repairs to the a/c system on my 300SD.

From a non-functioning, blocked system to one which cools nicely was a matter of several weeks' correspondence and much time spent by Larry Bible in helping me fix multiple problems.

Well, this thing fought me to the bitter end.

After replacing a blocked expansion valve (boy, is it tough to get at that top left hand nut, or what?), the receiver-drier, the gauge connectors, putting dye in the system, I got the thing working only to have the condenser blow.

Before vacuuming the system out thoroughly I thought I would verify the pressures on my 560SEL (also R134a) as a cross check - 19 low, 135 high, which equates with 2.2 x Ambient temp in F (I did this at 60F - cool morning). As I detached the low side, the blasted valve got stuck open and I lost the R134a from the 560SEL.....so now I have another system to fix, albeit at little labor expenditure.

I vacuumed the 300SD out thoroughly and recharged to the same 19 low, 135 high. The weight of R134a in the system was 1 lb 8 ozs, which is correct for the R4 compressor, so weight and pressures correlated nicely. Larry has advised that weight is the way to go, but it's nice to have a cross check.

So, one receiver-drier, one expansion valve, one blasted temp switch as the original would not fit the new r/d and one condenser later, I have a functioning a/c system on the 300SD.

Larry - this would not have been possible without your help and selfless assistance and I am deeply grateful. In the process, I learned about how things go together on a car a/c system (I am reasonably comfortable with the physiscs of a/c and related concepts) but now I know how to fix it in a car. Sure hope I never have to replace an evaporator, though!